The present invention relates generally to the field of spinal fusion and specifically spinal fusion devices and associated methods.
The human spine comprises a series of alternating vertebrae and discs. Herniated discs, bone spurs, degenerated discs, or other conditions that result in nerve root or spinal cord compression can cause severe pain and dysfunctional spinal conditions. Such conditions include, but are not limited to, axial back or neck pain, cervical or lumbar radiculitis/radiculopathy, cervical or lumbar deformity, cervical or lumbar spondylosis, stenosis, discogenic pain, myelopathy, and headaches. Spinal fusion is a common surgical technique to alleviate this pain and requires the permanent joining of two adjacent vertebrae via a bone graft (supplemental bone tissue). In an interbody spinal fusion procedure, a surgeon will first remove a troublesome disc from between two vertebrae and replace the disc with a bone graft. It is the goal of this procedure for the bone graft to work in conjunction with the natural tissue in the vertebrae to form new bone material, fusing the two vertebrae together. If the fusion does not take, i.e., bone does not completely grow across the interspace between vertebrae, this could result in pain for the patient, hardware failure, and/or a need for further surgery.
Frequently, spinal instrumentation will be included in the fusion procedure. Various implants have been developed to improve the quality of the grafting process and ensure a successful fusion. It is important that such implants (i) provide a vehicle to hold the bone graft material in place between the two vertebrae, (ii) immobilize the vertebra-graft-vertebra segment so that fusion may occur, (iii) maintain proper disc height for the removed disc, and (iv) maintain or restore proper alignment of the spine.
One implant device uses a combination of a separate plate and spacer. The spacer is prepackaged with bone or bone substitute and is inserted into the space between the vertebrae, and a plate that accepts four screws (two into each vertebrae) is fastened over the spacer. However, the plates used in these implants (i) can impinge upon adjacent discs or vertebrae, (ii) can pose alignment difficulties, and (iii) require more dissection and retraction during the surgery.
Another implant utilizes a plate preassembled with a spacer. These implants have the advantages of less dissection, ease of insertion, and a speedier surgical procedure. However, they have significant drawbacks in that they generally only have one screw per vertebrae, and the bone graft material must be pre-inserted into the spacer, which would not allow for in situ adjustments. Additionally, with low profile devices where the plate does not extend over the anterior surface of the vertebral bodies, the screws must be inserted at difficult angles in these apparatuses.